Conventional wire bonding (WB) is a method of making interconnections with a semiconductor chip. A bonding wire is generally made from one of the following materials: gold, aluminum or copper. Wire diameters typically start at around 15 μm and can be up to several hundred micro-meters for high-powered applications.
There are two main classes of wire bonding: Ball bonding and Wedge bonding.
Ball bonding is usually restricted to use of gold and copper wire, and usually requires heat to make a respective bond. Wedge bonding can use either gold or aluminum wire. When gold is used in wedge bonding, heat is required to make a respective bond.
In either type of wire bonding, the wire is typically attached using some combination of heat, pressure, and ultrasonic energy to make a weld. Wire bonding is generally considered the most cost-effective and flexible interconnect technology. Wire bonding is thus widely used to assemble the vast majority of semiconductor packages.
Conventional memory chips in a so-called “Multi-Chip-Package (MCP)” system are often interconnected using a parallel interconnection scheme. This “multi-drop” connection method includes interconnecting the memory chips in a manner such that address and data information and control signals are coupled to the chips in a parallel manner using common signal buses. For example, each memory chip can include multiple inputs and outputs to accommodate a parallel transfer of control information, address information, and data through an interconnected set of memory devices.
Various three-dimensional Package-on-Packages (PoPs) have recently been developed in the semiconductor memory industry in efforts to, for example, satisfy demand for increased memory density and functionality. In accordance with some example developments, a conventional three-dimensional package-on-package may be fabricated as follows: After manufacturing a wafer and separating the wafer into a plurality of individual chips, a corresponding chip can be attached and electrically connected to a substrate. The chip can be encapsulated with a molding resin to produce a package. A so-called package-on-package can be created by stacking the packages. These package-on-packages employ a lead frame, or a substrate such as, for example, a tape circuit board or a printed circuit board. An interconnect method such as, for example, a Wire-Bonding (WB), Tape-Automated-Bonding (TAB), or flip-chip-bonding, can be employed to establish electrical connections between the chip and the substrate.
Unfortunately, the different known methods of fabricating PoPs requires use of complex fabrication processes. Moreover, these PoPs are quite large compared to a standard chip, thereby reducing the mounting density on the external apparatus. Further, PoPs can include many interconnected chips with long signal transmission routes. Long routes may, for example, cause signal delays which could be expected to lower system performance.
However, stackings of memory chips into three-dimensional stacked-chip Multi-Chip-Packages (MCPs) on wafer-level or chip-level have the advantage of simple structures, smaller sizes, and simple manufacturing processes. Further, a multi-chip-package at the wafer-level may prevent signal delay.
It is possible to classify multi-chip-packages into two types. One is a multi-chip-package formed by stacking different types of chips, thereby achieving multi-functionality. The other is a multi-chip-package formed by stacking the same types of chips, thereby expanding the memory capacity.
NAND Flash memory is a commonly used type of non-volatile memory in widespread use as mass storage for consumer electronics, such as digital cameras and portable digital music players for example.
The density of a presently available NAND Flash memory chip can be up to 32 Gbits (i.e. 4 GBytes), which is suitable for use in popular USB Flash drives since the size of one chip is small. However, recent demand for consumer electronics devices with music and video capabilities has spurred demand for ultra-high capacities to store the large amounts of data, which cannot be met by the single NAND Flash memory chip. Therefore, multiple NAND Flash memory chips have been interconnected with each other into a storage system to effectively increase the available storage capacity. In certain cases, Flash storage densities of 250 GB or more may be required to accommodate data storage needs.